Method for manufacturing a solid housing

ABSTRACT

A method for manufacturing a solid housing, in particular a valve housing for an electromagnetically operable valve, includes the following operations or steps: a) providing a base element made of a magnetic or magnetizable material, b) carburizing and/or nitride-hardening of at least one subarea of the base element by diffusion of carbon and/or nitrogen under thermal treatment for forming a non-magnetizable structure in the area of the diffusion zone, and c) finishing the base element so created until an intended geometry of the housing is achieved. The housing is suitable in particular for use in fuel injectors in fuel injector systems of mixture-compressing spark-ignition internal combustion engines.

FIELD OF THE INVENTION

The present invention is directed to a method for manufacturing a solidhousing.

BACKGROUND INFORMATION

FIG. 1 shows a fuel injector from the related art having a traditionalthree-part design of an inner metal flow guidance part and housingcomponent at the same time. This inner valve tube is formed by an inletconnection piece forming an internal pole, a nonmagnetic intermediatepart and a valve seat carrier holding the valve seat, as explained ingreater detail in the description of FIG. 1.

German patent document DE 35 02 287 A1 discusses a method formanufacturing a hollow cylindrical metal housing having two magnetizablehousing parts including a nonmagnetic housing zone between them, forminga magnetic isolation between the housing parts. This metal housing ispremachined in one piece from a magnetizable blank down to an excessoutside diameter, a ring groove being cut in the inside wall of thehousing in the width of the desired middle housing zone. In the case ofa rotating housing, a nonmagnetizable filler material is filled into thering groove, while the ring groove area is heated up, and rotation ofthe housing is continued until the filling material solidifies. Thehousing is then turned on the outside down to the final dimension of theoutside diameter, so that there is no longer a connection between themagnetizable housing parts. A valve housing manufactured in this way maybe used, e.g., in solenoid valves for antilock brake systems (ABS) inmotor vehicles.

In addition, methods for manufacturing a solid core for fuel injectorsfor internal combustion engines are known from DE 42 37 405 C2 (FIG. 5of the document). These methods are characterized in that a one-piecesleeve-shaped magnetic martensitic workpiece which is provided directlyor via prior transformation processes undergoes a local heat treatmentin a middle section of the magnetic martensitic workpiece to convertthis middle section into a nonmagnetic, austenitic middle section.Elements forming austenite and/or ferrite molten by laser during thelocal heat treatment are alternatively added at the site of the heattreatment to form a nonmagnetic, austenitic middle section of the solidcore.

SUMMARY OF THE INVENTION

The method according to the present invention for manufacturing a solidhousing having the characterizing features of the main claim has theadvantage that housings having a magnetic isolation may be reliably massproduced in a particularly simple and inexpensive method.

Due to the simplicity of the individual components, the complexity andexpenditure in terms of special tools are reduced in comparison with theknown manufacturing methods.

It is also an advantage that it is possible to design the geometry ofthe housing itself with great flexibility, in terms of length, externaldiameter and shoulders, for example.

Advantageous refinements of and improvements on the method characterizedin the main claim are possible through the measures characterized in thesubclaims.

It is particularly advantageous to let the carburizing and/ornitride-hardening of the at least one subarea of the base element takeplace in a C- and/or N-containing environment, the appropriate thermaltreatment being carried out at high temperatures or being plasma-inducedin order to enable diffusion of the carbon or nitrogen molecules intothe edge layer of the base element.

Exemplary embodiments of the present invention are shown in simplifiedform in the drawing and explained in greater detail in the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fuel injector according to the related art having athree-part inner metal valve tube as a housing.

FIG. 2 schematically shows method steps of a method according to thepresent invention for manufacturing a solid housing.

FIG. 3 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 4 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 5 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 6 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 7 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 8 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 9 also schematically shows method steps of a method according tothe present invention for manufacturing a solid housing.

FIG. 10 shows a schematic section from an injector having a housingmanufactured according to the present invention.

DETAILED DESCRIPTION

Before describing the method steps of the method for manufacturing asolid housing according to the exemplary embodiments and/or examplarymethods of the present invention with reference to FIGS. 2 through 9, afuel injector according to the related art will be explained in greaterdetail below with reference to FIG. 1 as a possible insert product for ahousing manufactured according to the exemplary embodiments and/orexamplary methods of the present invention.

The electromagnetically operable valve as shown in FIG. 1, for example,in the form of a fuel injector for fuel injection systems of internalcombustion engines operating by spark ignition of a compressed fuel-airmixture has a tubular core 2 surrounded by a magnet coil 1, functioningas the fuel inlet connection piece and internal pole. The tubular corehas a constant outside diameter over its entire length, for example. Acoil body 3 having steps in the radial direction receives a winding ofmagnet coil 1 and, in combination with core 2 permits a compact designof the fuel injector in the area of magnet coil 1.

A tubular nonmagnetic metallic intermediate part 12 is joined tightly bywelding to a lower core end 9 of core 2 concentrically with alongitudinal valve axis 10 and surrounds core end 9 axially in part. Atubular valve seat carrier 16 is fixedly joined to intermediate part 12and extends downstream from coil body 3 and intermediate part 12. Anaxially movable valve needle 18 is situated in valve seat carrier 16. Aspherical valve closing body 24 provided on downstream end 23 of valveneedle 18 has, for example, five flat areas 25 on its circumference toallow fuel to flow past it.

The fuel injector is operated electromagnetically by the known method.The electromagnetic circuit having magnet coil 1, core 2 and an armature27 is used to produce the axial movement of valve needle 18 and thus toopen the valve against the spring force of a restoring spring 26 and/orfor closing the fuel injector. Tubular armature 27 is fixedly joined,e.g., by a weld to one end of valve needle 18 facing away from valveclosing body 24 and is aligned with core 2. A cylindrical valve seatbody 29 having a fixed valve seat 30 is tightly mounted by welding intothe downstream end of valve seat carrier 16 facing away from core 2.

Spherical valve closing body 24 of valve needle 18 cooperates with valveseat 30 of valve seat body 29 tapering in the form of a truncated conein the direction of flow. On its lower end face, valve seat body 29 isfixedly and tightly joined to an spray orifice disk 34 designed in theform of a pot, for example, the joint being formed by a weld createdusing a laser, for example. At least one, e.g., four spray orifices 39shaped by erosion or punching are provided in spray orifice disk 34.

To direct the magnetic flux to armature 27 for optimum operation ofarmature 27 when current is applied to magnet coil 1 and thus for secureand accurate opening and closing of the valve, magnet coil 1 issurrounded by at least one, for example, bow-shaped guide element 45 andfunctions as a ferromagnetic element, at least partially surroundingmagnet coil 1 in the circumferential direction and is in contact withcore 2 at one end and with valve seat carrier 16 at its other end and isjoinable to them by welding, soldering and/or gluing, for example. Core2, nonmagnetic intermediate part 12 and valve seat carrier 16, which arefixedly joined together and extend as a whole over the entire length ofthe fuel injector, form an inner metal valve tube as the basic structureand thus also the housing of the fuel injector. All other functiongroups of the valve are situated inside or around the valve tube. Thisarrangement of the valve tube is a classic three-part design of ahousing for an electromagnetically operable unit such as a valve havingtwo ferromagnetic, i.e., magnetizable housing areas which are isolatedmagnetically from one another by a nonmagnetic intermediate part 12 foreffective conduction of the magnetic circuit lines in the area ofarmature 27 or are at least joined together by a magnetic restriction.

The fuel injector is mostly surrounded by a plastic sheathing 51 whichextends starting from core 2 axially over magnet coil 1 and the at leastone conducting element 45 to valve seat carrier 16, at least oneconducting element 45 being completely covered axially andcircumferentially. An integrally molded electric plug 52, for example,is part of this plastic sheathing 51.

Using the method steps of the method for manufacturing a solid housingaccording to the present invention as schematically indicated in FIGS. 2through 9, it is possible in an advantageous manner to manufacturehousings 66 having thin walls for a variety of purposes, which may befor electromagnetically operable valves that may replace a three-partvalve tube as described above and to do so in a particularly simple andinexpensive manner.

In a first method step (FIG. 2), for example, a cylindrical base element55 is provided, from which housing 66 is to be manufactured, and whichis made of a magnetic or magnetizable material and is, for example,ferromagnetic or has a ferritic or a martensitic material structure.Base element 55 may initially be solid and may be obtained from long barmaterial for a particularly effective manufacture of a plurality ofhousings 66, for example. For obtaining local magnetic properties, athermal treatment is carried out in a subarea of base element 55 inwhich carbon and/or nitrogen is/are individually or in combinationdiffused into the material of base element 55. In order to achieve achange in the magnetic properties in only a small selected area, theremaining area of base element 55 is provided with a two-part pot-shapedcover 57. Cover 57 protects base element 55 from diffusion of carbonand/or nitrogen outside diffusion zone 58 to be treated. Carburizing ornitride-hardening of base element 55 in the area of diffusion zone 58takes place by placing base element 55 in C- and/or N-containingenvironment 59 until a non-magnetizable, in particular austenitic,structure is formed in diffusion zone 58. Carbon and/or nitrogenmolecules diffuse at high temperatures or by induced plasma into theedge layer of the magnetic material.

Covering 57 of the areas of base element 55 not to be affected may, asshown in FIG. 2, be carried out via a mechanical protective cover oralso via a coating, e.g., using a thermal protection paste or thematerial of base element 55 itself which is suitably contoured for thispurpose (FIGS. 7 through 9).

For example, diffusion zone 58, which is formed in the middle area ofbase element 55, ultimately represents the area of the magneticisolation, as FIG. 3 shows.

Due to the diffusion of carbon and/or nitrogen into base element 55,three lengthwise zones are created which each directly successively havedifferent magnetic properties due to the thermal treatment in connectionwith the addition of carbon and/or nitrogen. Both outer zones of baseelement 55 have the same magnetic properties while the middle diffusionzone 58 assumes a non-magnetizable or poorly magnetizable, in particularaustenitic or partially austenitic, material structure having no or onlyvery low saturation magnetization and is isolated from both outer zones(FIGS. 4 and 6).

While an inner longitudinal opening 60 for forming a tubular housing 66(FIGS. 3 and 4) is made into solid base element 55, for example, onlysubsequently to the thermal treatment with local carburizing and/ornitride-hardening, it is also conceivable to use an already tubular baseelement 55 having an inner longitudinal opening 60 as the starting blankand provide it locally with a diffusion zone 58 at an intended spot(FIGS. 5 and 6). A base element 55 which is already tubular prior to thethermal treatment has the advantage that a diffusion of theaustenite-stabilizing elements C and/or N is possible from the outerwall and the inner wall of base element 55.

As mentioned above, cover 57 may be formed by the material itself ofbase element 55 which must be suitably contoured for this purpose. Basedon FIGS. 7 through 9 it is explained what such a contour of base element55 may look like. For example, a circumferential recess 62, similar to agroove or a cut-in, is provided in the area of the later intendeddiffusion zone 58, base element 55 having a larger external diameterthan housing 66 which is subsequently made from it. Edge zone 63 of baseelement 55 is now consecutively magnetically influenced in C- and/orN-containing environment 59. Base element 55 is reworked subsequently tothe thermal treatment by removing edge zone 63 largely down to recess62. This may be carried out, for example, by using known mechanical ornon-mechanical methods for removal, such as milling, grinding, thermalremoval via electrical discharge machining, electron beam or laser beam,electrochemical machining (ECM, etching) or chemical removal. As FIG. 9shows, removal of edge zone 63 is carried out until there is a housing66 which has diffusion zone 58 exclusively in an intended area havingchanged material properties. The material thicknesses are not shown toscale.

Here also, an inner longitudinal opening 60 for forming a tubularhousing 66 may be made into solid base element 55 either prior orsubsequently to the thermal treatment via local nitride-hardening and/orcarburizing.

Prior to installation of housing 66 in a valve or other assemblies,housing 66 is subjected to a finishing operation to have solid housing66 in an intended geometry. In the event of using a housing manufacturedaccording to the exemplary embodiments and/or examplary methods of thepresent invention in a fuel injector, it may be an advantage tospecifically form housing 66 using technical manufacturing measures suchas ironing, tumbling, swaging, flanging and/or flaring. Housing 66represents a component which, in a known fuel injector according to FIG.1, may completely take on the functions of the valve tube made up ofcore 2, intermediate part 12, and valve seat carrier 16 and may thusextend over the entire length of a fuel injector.

FIG. 10 shows a schematic section from a fuel injector having housing 66manufactured according to the exemplary embodiments and/or examplarymethods of the present invention which is installed as a thin-walledsleeve in the valve and surrounds core 2 and armature 27 radially and inthe circumferential direction and is itself surrounded by magnet coil 1.It becomes clear that the area of diffusion zone 58 of housing 66, whichhas changed magnetic properties and is, for example, austenitic, islocated in the axial extension area of a working air gap 70 between core2 and armature 27 in order to guide the magnetic circuit lines optimallyand effectively in the magnetic circuit. Instead of clamp-shaped guideelement 45, shown in FIG. 1, the outer magnetic circuit component isdesigned as magnet pot 46, the magnetic circuit between magnet pot 46and housing 66 being closed via a cover element 47. The method accordingto the present invention makes it also possible to change housings 66having greater wall thicknesses locally in their magnetic properties sothat a higher internal pressure resistance is ensured despite aminimized magnetically active area in favor of the magnetic force.

The exemplary embodiments and/or examplary methods of the presentinvention is by no means limited to use in fuel injectors or solenoidvalves for antilock brake systems but instead it also pertains to allelectromagnetically operable valves of different areas of applicationand in general all solid housings in units in which zones of differingmagnetism are necessary in succession. Thus not only housing 66 havingthree successive zones may be manufactured by the method according tothe exemplary embodiments and/or examplary methods of the presentinvention but also housings 66 having more than three zones.

1-11. (canceled)
 12. A method for manufacturing a solid valve housingfor an electromagnetically operable valve, the method comprising: a)providing a base element made of a magnetic material or a magnetizablematerial; b) at least one of carburizing and nitride-hardening at leastone subarea of the base element by diffusing at least one of carbon andnitrogen under thermal treatment for forming a non-magnetizablestructure; and c) finishing the resulting base element until an intendedgeometry of the housing is achieved; wherein the housing includes atleast three zones and two directly adjacent zones have differentmagnetic properties.
 13. The method of claim 12, wherein the baseelement is ferromagnetic, has a ferritic material structure or has amartensitic material structure.
 14. The method of claim 12, wherein thebase element is provided in cylindrical form.
 15. The method of claim14, wherein the base element is provided prior to the thermal treatmentand a change of magnetic properties of a solid cylindrical form or ahollow cylindrical form having an inner longitudinal opening.
 16. Themethod of claim 12, wherein at least one subarea of the base element isat least one of carburized and nitride-hardened in at least one of aC-containing and an N-containing environment.
 17. The method of claim12, wherein a diffusion zone, which forms the non-magnetizable zone, iscreated by diffusing at least one of C and N thereinto.
 18. The methodof claim 17, wherein the base element is provided with a cover outsidethe diffusion zone.
 19. The method of claim 18, wherein the cover is oneof a mechanical protective cover and a coating which is applied using athermal protection paste.
 20. The method of claim 12, wherein the baseelement is contoured so that the base element is at least one ofcarburized and nitride-hardened throughout, so as to create an entirelymagnetically influenced edge zone.
 21. The method of claim 20, wherein agroove-like recess is provided on the base element in whose place alocal diffusion zone solely remains after removal of the edge zone. 22.The method of claim 12, wherein finishing of the base element is donevia at least one of ironing, tumbling, swaging, flanging, and flaring.